The present invention relates to pipe supporting dam assemblies and methods for pipeline constructions, being particularly useful for preventing the flow of groundwater from following the path along the outside of the sloping pipe and washing away bedding of backfill material in the pipeline trench which can cause structural collapse or the consequent build-up of fines of the backfill that can cause heaving of the upper pavement surface, or silt pollution at the point of pipe-to-surface penetration.
In such pipeline construction for sewer and drainage systems and the like, PVC or other pipe conduits are installed in the earth in a trench and covered with stone bedding and then the backfill material to give a solid and compact base to the pipe installation. In order to have bedding material that will compact, material that has a very low plasticity (which allows water to transmit through it freely) has to be used. For example, bedding material used for PVC pipe is generally washed stone which has high compactibility and it also has voids that allow water to move through it freely. Especially in a soil fill that has a high plasticity content or index, groundwater seeks the easiest route through the stone, seeking its own level, and will follow the slope of the pipe along the outside surface thereof. When this happens, the bedding and other material on top of the pipe, which normally contains fines, generally sand, is subject to water picking up these fines in the bedding or other material packed around the pipe and carrying them along either the bottom of the trench or along the outside surface of the pipe, frequently developing a build-up that can cause a structural fill collapse in the road.
Prior to the present invention, there have been two principal technologies for trying to mitigate against such water flow effects. One has been to pour concrete around the pipe, but this creates an undue stress on the pipe, especially with ground movement; and, in addition, the concrete does not seal to the PVC pipe so the water can still flow along the outside surface of the pipe. Another technique has been to create an earth or a clay dam, where the clay is actually imported to the site and packed around the pipe; but this also leaves much to be desired since its effectiveness depends upon correct installation and because clay has a high plasticity index which results in the development of voids, with the clay, moreover, not actually sealing to the pipe but allowing the groundwater to flow along the outside of the pipe.